The present invention is directed to a turret mooring system which comprises a turret that is rotatably supported in the moon pool of a vessel by at least an upper bearing assembly. More particularly, the invention is directed to a bearing support assembly which isolates the upper bearing assembly from deflections of the vessel.
Turret mooring systems are commonly used to anchor a vessel to the sea floor. Internal turret mooring systems typically comprise a turret which is rotatably supported in a moon pool that is formed in the hull of the vessel between the bow and the stern. The turret is often supported by both an upper bearing assembly which is connected between the upper end of the turret and the top of the moon pool and a lower bearing assembly which is connected between the lower end of the turret and the bottom of the moon pool. The upper bearing assembly typically comprises a combination axial and radial bearing which is capable of transmitting both the vertical and horizontal mooring loads from the turret to the vessel. The lower bearing assembly usually comprises a radial bearing which transmits only the horizontal mooring loads from the turret to the vessel.
A vessel in the open sea is often affected by waves and swells which can cause the vessel to hog and sag. As the vessel hogs and sags, the normally circular cross section of the moon pool deflects into alternating oval configurations. Since the vessel reacts somewhat like a beam in bending, these deflections are greatest at the top of the moon pool, which is normally where the upper bearing assembly is connected. In addition, turret mooring systems are typically designed to provide a clearance between the lower bearing assembly and the turret. As a result, the horizontal mooring loads will cause the turret to pivot about a horizontal axis located near the upper bearing assembly. Unless means are provided to isolate the upper bearing assembly from the deflections of the moon pool and the pivoting of the turret, these displacements may damage the upper bearing assembly and interfere with the operation of the turret mooring system.
In certain prior art turret mooring systems, bearing support assemblies comprising elastomeric or steel springs have been employed to isolate the upper bearing assembly from the deflections of the moon pool and to allow the turret to pivot about a horizontal axis. However, these bearing support assemblies contain many parts, require frequent maintenance and are expensive.